This invention relates generally to internal combustion engines. More specifically, it relates to a system for controlling the timing, or phasing, of the valves of such engines.
The ability to adjust the timing of the intake and exhaust valves of internal combustion engines has been shown to improve engine performance. In an engine in which the intake and exhaust valves are operated mechanically by means of a camshaft that is driven by the engine crankshaft, the task of performing valve timing functions requires the use of a prime mover acting through a phasing mechanism on the camshaft to vary the phasing of the camshaft with respect to that of the crankshaft. Camshaft phasing is sensed by a sensor s that closed-loop control of the camshaft phasing can be obtained.
For optimum performance it has been found desirable for the valve timing function to be correlated with other engine timing functions. These other timing functions, such as fuel and ignition timing functions, are performed by the engine electronic control unit (ECU). The engine ECU typically contains a microprocessor that acts upon various inputs to calculate optimum values for fuel and ignition control functions. The engine ECU can also calculate the appropriate camshaft phasing, but if called upon to also exercise closed-loop control over the camshaft phasing, the typical engine ECU may lack sufficient power to do so. While a more powerful ECU could be employed, such a solution may not be the optimal one when all considerations relating to the mass production of various ECU-controlled engines are taken into account.
The present invention relates to a new and unique system for performing valve timing, or phasing, functions which avoids introducing complications into the engine ECU. The invention envisions a second ECU, hereinafter called a modular position controller (MPC), that is responsible for the active closed-loop control of valve timing, or phasing. Moreover, the invention contemplates that the operation of the MPC be correlated with that of the engine ECU by placing the PPC in communication with the engine ECU such that the engine ECU provides valve timing, or phasing, information to the MPC in a particular format. The MPC is capable of acting on this information to perform the closed-loop control of the valve timing.
In the disclosed embodiment where a camshaft phasing control is used, the ECU provides phasing information via a single wire, and this is an important advantage of the invention. In the disclosed preferred embodiment the information is provided as a rectangular waveform on this single wire. The waveform contains crankshaft position information, in the form of a top dead center (TDC) signal, and also a desired phasing for the camshaft. The rectangular waveform signal has the leading edge synchronized with TDC and the width of the pulse as measured from TDC corresponds to the desired camshaft phasing.
The foregoing features, advantages, and benefits of the invention, along with others, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at this time for carrying out the invention.